1. Field of Invention
This invention relates to synthetic surgical devices having improved properties made from copolymers of glycolide and .epsilon.-caprolactone and, more particularly, to oriented filaments and sutures prepared from such polymers and to methods of manufacturing such polymers.
2. Description of the Prior Art
Homopolymers and copolymers of lactide and glycolide are well known in the preparation of synthetic absorbable sutures as disclosed, for example, in U.S. Pat. Nos. 3,636,956; 2,703,316; 3,468,853; 3,865,869, and 4,137,921. Also, in U.S. Pat. No. 3,867,190, it is known to include certain cylic comonomers with glycolide including .epsilon.-caprolactone. In fact, the use of cylic ester monomers in the formation of polyesters for the fabrication of synthetic surgical articles is well known in the art. The conventional polymerization method of forming polymers of the cylic esters is through ring opening polymerization. In U.S. Pat. No. 4,300,565, there is disclosed surgical articles fabricated from synthetic absorbable copolymers formed by copolymerizing glycolide with a cylic ester monomer in a specific manner. Hence, it should be appreciated that broadly copolymers of .epsilon.-caprolactone and other cyclic esters, such as lactide or glycolide, are well known and described in the art as well as are various methods for their production.
The synthetic absorbable sutures have gained considerable acceptance in the surgical field; however, the "handleability" or the compliance; i.e., flexibility and "limpness", has not always been considered satisfactory in monofilament configurations. It is believed that monofilament constructions are more suitable for surgical uses than the multifilament or braided configurations as they tend to produce less infection and trauma at the wound closure site. However, the monofilaments tend to be stiffer and harder to handle than the braided configuration of the same diameter. Over the years, various polymer combinations have been tried in an attempt to obtain the desired very delicate interplay between the properties of suture absorbability, in vivo strength retention, initial knot strength, and high compliance or low modulus. These desired properties, other than absorbability, are obtained in some suture materials; for example, in those described in commonly assigned copending patent applications Ser. No. 311,829 filed Oct. 16, 1981, and Ser. No. 338,407 filed Jan. 8, 1982. The suture materials described have the desired strengths, compliance and flexibility but are not absorbable and, hence, are limited in their use. To the best of our knowledge the only synthetic, absorbable sutures which in some instances may have the properties as described above are those made from polydioxanone as described in U.S. Pat. No. 4,052,988.
It should be appreciated, that to design molecular chains needed for the production of highly compliant absorbable materials, an obvious route is to copolymerize suitable comonomers or mixtures of pre-polymers and monomers following procedures similar to those used in the formation of compliant non-absorbable sutures. However, such is not the case for those polymers are of the AA-BB non-absorbable type. Furthermore, copolymerizing comonomers of glycolide and .epsilon.-caprolactone following the teaching of U.S. Pat. No. 3,867,190 which describes the copolymers containing 15% or less of the .epsilon.-caprolactone moieties does not produce compliant materials. Copolymers containing less than 15% caprolactone are random in nature and the monofilaments made therefrom display high modulus and low compliance. It is known that copolymers containing less than 85% glycolide moieties with random microstructure do not generally offer good fiber forming polymers because of their improper level of crystallinity. Hence it would be expected that copolymers containing more than 15% caprolactone sequences would have poor crystallinity and be virtually amorphous and unsuitable for the production of strong monfilament suture materials.